雙螺帽預壓滾珠螺桿之螺帽熱效應分析與垂直傳動性能改善研究

Analysis of Thermal Effect and Vertical Driving Performance Improvement for Preloaded Double Nut Ball Screw

洪邑(Yi Haung)

指導教授 ： 魏進忠

國立虎尾科技大學/工程學院/動力機械工程研究所/碩士(2015年)

摘要

滾珠螺桿為一高精度線性傳動之元件，在高速化與高軸向負荷的操作條件下，將使得螺帽內部的滾珠在軌道上因滑動現象所造成的磨耗導致預壓力下降，摩擦熱也會使螺帽內部的溫度上升，造成元件的熱膨脹，對於移動平台的傳動精度和穩定度有非常顯著的影響。本文分析不同滾珠對螺帽的接觸角度，並藉由有限元素分析軟體(Ansys Workbench)建立螺帽模型進行熱分析，比較提高接觸角前後的性能差異。根據滾珠螺桿運動學理論求得滾珠與螺帽間在不同接觸角下的正向力、摩擦係數、滑動速度等參數，分別計算滾珠螺桿在傳動時加、等、減速段的滾珠在軌道接觸面之平均熱通量，並將螺帽在往復運動過程中，所受到空氣對流冷卻的影響來設定螺帽與空氣以及與固定元件的熱傳邊界條件，將螺帽熱分析模型的結果將與實驗做驗證，預測螺帽達熱穩定後之溫度變化，探討不同接觸角和預壓力下降的溫升情況。
實驗機台使用垂直方向傳動之單軸螺桿測試機，分別使用兩種不同接觸角的滾珠螺桿進行測試，並於螺帽軌道上方和表面分別裝置熱電偶與應變規，以量測螺帽之溫度與應變的變化趨勢，並且使用扭力計來量測滾珠螺桿的傳動性能，再將實驗的性能表現與模擬之結果相互印證，發現較高接觸角設計之螺帽，在螺帽溫度的分布和傳動性能，具有較穩定的表現。藉由本研究螺帽熱模型分析之理論與實驗的趨勢相互驗證下有相同的變化，在未來可以利用該模型資料來建立不同操作條件下螺帽的穩態溫度經驗公式，應用於滾珠螺桿的螺帽接觸角的設計與熱變位補償機制之依據，提出新型滾珠螺桿的傳動性能最佳化設計。

關鍵字

滾珠螺桿 ； 雙螺帽 ； 摩擦熱 ； 熱膨脹 ； 有限元素分析 ； 接觸角

並列摘要

Ball screw is a high-precision and high performance linear drive of mechanical spares. When the ball screw is working in the high-speed and high axial load conditions, those will make the ball have high friction on the track of nut and dereasing the applied preload due to wear of raceway. Frictional heat affects also effect the rising temperature of nut ,which cause thermal expansion.Driving accuracy and stability of the transmission platform is thus affected with a very significant impact. In this paper, various contact angles of ball-nut contact area were analized by using of finite element analysis software (Ansys Workbench) to establish thermal analysing model of the nut . The difference of results are compared in high contact angle and the general contact angle 45-degree which is common used in industry. Set the boundary conditions based on the ball screw kinematics theory.Normal force, friction coefficient and sliding speed between the ball and the nut are obtained at different contact angles.They are applied to calculate the average heat flux at the ball contact surfaces of track when ball screw driving at acceleration, constant speed and deceleration.Air and the nut’s heat transfer boundary conditions are colled by air convection when the nut in a reciprocating motion.Results of the nut thermal analysis were confirmation with experiment and make sure it can predict the rising temperature when the nut is at heat stability.Based on the model, nut designed in different contact angles and preload effect can be studied in temperature rising effect.
In this study, the experimental machine using a vertical axis testing the nut with two different contact angles. And the surface of the nut on the track were installed thermocouples and strain gauges. Measuring trends of temperature and strain in the nut and the torque meter used to record the ball screw driving torque.Comparing the performance of experimental and simulation results , it found that higher contact angle design at the nut has a more stable performance of temperature distribution in the nut and driving torque. Theoretical analysis of the nut thermal model and experimental results have the same trends by this study. This model can be used in the future to establish the thermal steady-state temperature of the nut and propose the empirical formulas under the different operating conditions. It also can be applied to design optimal contact angle for structural and thermal displacement compensation mechanism of the ball screw nut. A a new kind of design for thermal stable ball screw can thus be designed.

並列關鍵字

Ball screw ； Double Nuts ； Friction Heat ； Thermal Expansion ； Finite Element Analysis ； Contact Angle

參考文獻

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